Proximity projector having a dust-proof cover

ABSTRACT

A proximity projection-type projector includes a housing; a dust-proof cover arranged on a top portion of the housing; and a projection unit arranged within the housing. The projection unit projects projection light though the dust-proof cover on the housing toward a screen disposed outside the housing. An anti-reflection film forms a light incident surface of the dust-proof cover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 12/642,280, filed Dec. 18, 2009, which claims priority toJapanese Application No. 2008-332967, filed Dec. 26, 2008 and JapaneseApplication No. 2008-332966, filed Dec. 26, 2008. The forgoing patentapplications are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates a projector, and particularly to atechnology of a projector including a cover portion that protects aprojection unit.

2. Related Art

A projector that projects light on a screen to display an image includesa light projection system in a housing. The performance of theprojection system is significantly degraded in some cases due to dust,dirt, and other factors. To protect the projection system from dust anddirt, a configuration in which the housing includes a light-transmissivecover portion has been proposed (see JP-A-2004-12749, JP-T-2008-522229,JP-A-2008-107801, and JP-A-2008-165202, for example).

Most of the light projected from the projection system passes throughthe cover portion and is projected on the screen, but part of the lightis reflected off the light-incident surface of the cover portion. Theratio of the amount of light reflected off the cover portion to thetotal amount of light incident thereon, that is, the reflectance, varieswith the angle of incidence of the light that impinges on thelight-incident surface. The reflectance of the light-incident surfaceincreases as the angle of incidence increases. The light projected fromthe projection system may impinge on the light-incident surface at avariety of angles. When the reflectance increases, the amount of lightthat can reach the screen decreases, and the image brightness decreasesaccordingly. Therefore, among the projection light incident on the coverportion, the projection light incident at a large angle of incidencedisadvantageously forms an image having reduced brightness.

To reduce the amount of reflection off the light-incident surface, it isconceivable to form an anti-reflection film (AR coating) over thelight-incident surface of the cover portion. In this case, however, asignificantly large number of coating layers is required to achieve ananti-reflection capability across a wide range of angle of incidence,resulting in increase in cost.

On the other hand, there is what is called a proximity projection-typeprojector capable of projecting wide-angle light from a position closeto a screen. Since a proximity projection-type projector uses wide-anglelight, the range of the angle of incidence of the light incident on thecover portion increases, and hence the projection light tends to beincident at a large angle of incidence. Therefore, a proximityprojection-type projector, in particular, suffers from significantreduction in image brightness due to the angle of incidence of the lightincident on the cover portion.

SUMMARY

An advantage of some aspects of the invention is to provide a projectorincluding a cover portion capable of protecting a projection system andreducing the loss of light due to the reflection off the light-incidentsurface of the cover portion to prevent reduction in image brightness ata low cost.

A projector according to an aspect of the invention includes aprojection unit that projects projection light toward an illuminatedsurface, a housing that houses the projection unit and has an openingthat allows the projection light to exit outward, and a cover portionthat blocks the opening and transmits the projection light. A pluralityof areas is set in the cover portion relative to the projection unit,and a process of changing the reflectance of the light-incident surfaceof the cover portion at which the projection light is reflected isperformed on each of the areas.

Since a plurality of areas is set in the cover portion and a process ofchanging the reflectance of the light-incident surface of the coverportion at which the projection light is reflected is performed on eachof the areas, the amount of reflection off the light-incident surface ofthe cover portion can be reduced. When the amount of reflection off thelight-incident surface is reduced, the loss due to the reflection andhence decrease in image brightness can be reduced.

In the projector including a projection unit that projects projectionlight toward an illuminated surface, a housing that houses theprojection unit and has an opening that allows the projection light toexit outward, and a cover portion that blocks the opening and transmitsthe projection light, it is preferable that a plurality of areas is seton the projection light-incident surface of the cover portion based onthe angle of incidence of the projection light, and an anti-reflectionprocess according to the angle of incidence of the projection light isperformed on each of the areas.

Since a plurality of areas is set on the light-incident surface of thecover portion and an anti-reflection process according to the angle ofincidence of the projection light is performed on each of the areas, theamount of reflection off the light-incident surface of the cover portioncan be reduced. When the amount of reflection off the light-incidentsurface is reduced, the loss due to the reflection and hence thedecrease in image brightness can be reduced. Further, since a processaccording to the angle of incidence is performed on each of the areas,it is not necessary to form a multilayer coating film on the entirelight-incident surface to achieve an anti-reflection effect across awide range of angle of incidence. The manufacturing cost can thereforebe reduced. The angle of incidence used herein is the angle between anormal to the light-incident surface in the position where a projectionlight ray of interest is incident and the projection light ray.

It is preferable that one of the plurality of areas is set as areference area on which a process of preventing the reflection of theprojection light incident at an angle of incidence within apredetermined range is performed, and a process of preventing thereflection of the projection light incident at a larger angle ofincidence is performed on an area spaced further apart from thereference area.

For example, when the projection light radially propagates, the angle ofincidence of the projection light increases with the distance from thelocation on the light-incident surface of the cover portion where theprojection light is incident at the smallest angle of incidence. In thiscase, when a process of preventing the reflection of the projectionlight incident at a larger angle of incidence is performed on an areaspaced further apart from the reference area and the projection light isincident on the reference area at the smallest angle of incidence, thereflection off the light-incident surface and hence the decrease inimage brightness can be effectively reduced.

It is preferable that the cover portion has a substantially rectangularshape in the plan view and the plurality of areas is formed by dividingthe light-incident surface into three in the longitudinal direction ofthe substantially rectangular shape. In this case, the reference area ispreferably the central area of the plurality of areas in thelongitudinal direction.

Dividing the light-incident surface into a large number of small areasin accordance with the angle of incidence of the projection light allowsthe amount of projection light that passes through the light-incidentsurface and reaches the illuminated surface to be increased. In thiscase, however, the anti-reflection and other processes are complicated,and the cost disadvantageously increases. In the case described above,since the light-incident surface is divided into three areas, whichcorrespond to the plurality of areas described above, theanti-reflection process is simplified and hence the cost can be reducedas compared to a case where the light-incident surface is divided into alarge number of areas.

It is preferable that the cover portion has a substantially rectangularshape in the plan view and the plurality of areas is formed by dividingthe light-incident surface into two in the short-side direction of thesubstantially rectangular shape. In this case, a process of preventingthe reflection of the projection light incident at an angle of incidencewithin a predetermined range is preferably performed on one of theareas, and a process of preventing the reflection of the projectionlight incident at an angle of incidence beyond the predetermined rangeis preferably performed on the other one of the areas.

Dividing the light-incident surface into a large number of small areasin accordance with the angle of incidence of the projection light allowsthe amount of projection light that passes through the light-incidentsurface and reaches the illuminated surface to be increased. In thiscase, however, the anti-reflection and other processes are complicated,and the cost disadvantageously increases. In the the case describedabove, since the light-incident surface is divided into two areas, whichcorrespond to the plurality of areas described above, theanti-reflection process is simplified and hence the cost can be reducedas compared to a case where the light-incident surface is divided into alarge number of areas. In particular, the area setting described aboveis effective when the light projected on an image portion where thebrightness does not decrease is incident only on one of the areas in theshort-side direction of the cover portion and the light projected onanother image portion where the brightness significantly decreases isincident only on the other one of the areas.

Further, since the light-incident surface is divided into two areas inthe short-side direction, for example, arranging a plurality of coverportions in the longitudinal direction allows anti-reflection processesto be performed on the plurality of cover portions at the same time. Inthis way, a large number of cover portions can be produced in a fewersteps, and the cover portions can be more efficiently manufactured.Alternatively, for example, a substrate in which cover portions aresuccessively connected in the longitudinal direction is prepared. Thesubstrate is divided into two areas in the short-side direction, andanti-reflection processes are performed. The processed substrate is thencut in accordance with the longitudinal dimension of the cover portion.A large number of cover portions can thus readily be manufactured. Inthis way, a large number of cover portions can be produced in a fewersteps, and the cover portions can be more efficiently manufactured.

It is preferable that the process of preventing the reflection of theprojection light is forming an anti-reflection film on thelight-incident surface. An anti-reflection process according to theangle of incidence of the projection light incident on each of the areascan be performed on each of the areas by forming an anti-reflectionfilm.

It is preferable that the anti-reflection films overlap with each otherat the boundary between adjacent ones of the areas. The overlap betweenthe anti-reflection films at the boundary between adjacent ones of theareas allows the brightness of an image displayed on the illuminatedsurface to change smoothly and hence prevents a viewer from recognizingthe boundary between the areas.

It is preferable that the projection unit includes a wide-angle lightforming reflector that converts the projection light into wide-anglelight. Since a projector including a wide-angle light forming reflector,that is, a proximity projection-type projector, uses wide-angle light,the projector tends to produce projection light incident at a largeangle of incidence and hence loose part of the projection light due toreflection. In the case described above, since an anti-reflectionprocess according to the angle of incidence is performed on each of theareas of the cover portion, the loss due to the reflection and hencedecrease in image brightness can be reduced.

In the projector including a projection unit that projects projectionlight toward an illuminated surface, a housing that houses theprojection unit and has an opening that allows the projection light toexit outward, and a cover portion that blocks the opening and transmitsthe projection light, it is preferable that the cover portion has asubstantially uniform thickness and includes a central portion andperipheral portions adjacent to the central portion, and the peripheralportions are bent toward the side where the projection light isincident.

Since the peripheral areas are bent toward the side where the projectionlight is incident, the angle of incidence of the projection light, forexample, when it radially propagates, in the peripheral portions can bereduced as compared to a case where the cover portion has an entirelyflat single light-incident surface. When the angle of incidencedecreases, the reflectance at which the projection light incident on theperipheral portions is reflected can be reduced, and hence the loss dueto the reflection off the light-incident surface of the cover portioncan be reduced. Therefore, the cover portion can not only protect theprojection unit from dust and dirt but also, for example, prevent thedecrease in brightness of an image displayed on a screen, which is theilluminated surface. The cover portion is configured not to have a lensfunction by forming it to have a substantially uniform thickness. Whenthe cover portion has no lens function, a slight positional error in aprocess of attaching the cover portion does not greatly affect thequality of a displayed image. This allows the assembly cost to bereduced and further allows the cover portion to be readily exchanged,whereby ease of maintenance of the projector can be improved. The angleof incidence used herein is the angle between a normal to thelight-incident surface in the position where a projection light ray ofinterest is incident and the projection light ray.

It is preferable that the central portion is formed of a flat surface.Since the central portion is formed of a flat surface, the manufacturingcost can be reduced as compared to a case where a curved surface isused. Further, since the projection light is incident on the centralportion of the cover portion at a small angle of incidence in aprojector in many cases, a problem of the decrease in image brightnesswill unlikely occur even when the central portion is formed of a flatsurface.

It is preferable that each of the peripheral portions is formed of aflat surface. No process of forming a curved surface needs to beperformed on each of the peripheral portions, whereby the manufacturingcost can further be reduced. Bending a flat member along the boundarybetween the central portion and each of the peripheral portions can forma bent cover portion formed of a flat central portion and flatperipheral portions. Even when each of the peripheral portions is formedof a flat surface, bending the cover portion along the boundaries allowsthe reflectance to decrease to a level at which the viewer does notsense decrease in the amount of light, whereby decrease in imagebrightness can be reduced.

It is preferable that the central portion has a substantiallyrectangular shape in the plan view, and the peripheral portions areconnected only to a pair of sides of the central portion that face eachother. Since the peripheral portions are connected only to a pair ofsides of the central portion that face each other, the cover portion canbe manufactured only by bending both sides of a flat plate havingentirely flat surface, whereby the manufacturing cost can be reduced.

It is preferable that the central portion is substantially parallel to apredetermined flat surface of the outer surfaces of the housing. Sincethe central portion is substantially parallel to a predetermined flatsurface of the outer surfaces of the housing, the projector can bedesigned with no constraint and the degree of design freedom can beincreased as compared to, for example, a case where a dome-shaped coverportion is employed. Further, when the central portion is completelyflush with the predetermined outer surface of the housing, the degree ofdesign freedom can be increased, and the cover portion can be integratedwith the housing. Integrating the cover portion with the housingcontributes to cost reduction because the number of assembly steps andthe number of parts are reduced. When the cover portion is integratedwith the housing, only the cover portion can transmit light by formingthe entire structure with a transparent member and painting the portionother than the cover portion.

It is preferable that each of the peripheral portions is substantiallyparallel to a predetermined flat surface of the outer surfaces of thehousing. Since each of the peripheral portions is substantially parallelto a predetermined flat surface of the outer surfaces of the housing,the projector can be designed with no constraint and the degree ofdesign freedom can be increased as compared to, for example, a casewhere a dome-shaped cover portion is employed. Further, when each of theperipheral portions is completely flush with the predetermined outersurface of the housing, the degree of design freedom can be increased,and the cover portion can be integrated with the housing. Integratingthe cover portion with the housing contributes to cost reduction becausethe number of assembly steps and the number of parts are reduced. Whenthe cover portion is integrated with the housing, only the cover portioncan transmit light by forming the entire structure with a transparentmember and painting the portion other than the cover portion.

It is preferable that the projection unit includes a wide-angle lightforming reflector that forms wide-angle light. In a projector includinga wide-angle light forming reflector, that is, a proximityprojection-type projector, when combined with a cover portion of relatedart, the reflection off the light-incident surface of the cover portionsignificantly reduces image brightness. The cover portion according tothe aspect of the invention having bent peripheral portions can reducethe angle of incidence of the projection light, reduces the reflectanceof the light-incident surface at which the projection light isreflected, and prevents decrease in image brightness.

It is preferable that the cover portion is inclined in such a way thatthe surface of the central portion through which the projection lightexits faces the illuminated surface. Since a proximity projection-typeprojector is installed below the screen, the projection light exitsthrough a top portion of the housing and travels toward the screenobliquely to some extent. Since the projection light is thus inclined,the angle of incidence of the projection light incident on thelight-incident surface of the cover portion increases. Since the coverportion according to the case described above is inclined in such a waythat the surface through which the projection light exits faces thescreen, the inclination of the cover portion can cancel the increase inthe angle of incidence of the projection light incident on thelight-incident surface of the cover portion due to the inclination ofthe projection light. Therefore, simply inclining the cover portion canprevent the decrease in image brightness.

It is preferable that the peripheral portions are bent and inclined tothe central portion by approximately 90 degrees. Since the peripheralportions are bent and inclined to the central portion by approximately90 degrees, the cover portion can be a compact structure in which onlysmall overhangs jut out from the central portion in the plan view. Thisstructure also contributes to the compactness of the projector. In aproximity projection-type projector, in particular, the wide-angleprojection light requires a large, wide cover portion to transmit allthe projection light when the cover portion is entirely flat. In thecase described above, since the peripheral portions are bent andinclined to the central portion by approximately 90 degrees, all theprojection light can be transmitted and the cover portion can be compactat the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers refer to like elements.

FIG. 1 is a perspective view showing how a projector according to afirst embodiment is used.

FIG. 2 is a transverse cross-sectional view showing a schematicconfiguration of the interior of the projector in the first embodiment.

FIG. 3 is a front cross-sectional view but does not show the interiorconfiguration of the projector in the first embodiment.

FIG. 4 describes a schematic configuration of a projection system in thefirst embodiment.

FIG. 5 shows a schematic configuration of an image formation opticalunit in the first embodiment.

FIG. 6 is a plan view of a dust-proof cover in the first embodiment.

FIG. 7 shows the relationship between the reflectance and the angle ofincidence of projection light incident on the dust-proof cover in thefirst embodiment.

FIG. 8 shows the reflectance of the dust-proof cover in the firstembodiment when a single anti-reflection film is formed on the entirelight-incident surface of the dust-proof cover and the projector usingthe dust-proof cover displays an image.

FIG. 9 shows the relationship between the positions on the dust-proofcover where projection light rays are incident and the positions on ascreen where the projection light rays are projected in the firstembodiment.

FIG. 10 is a plan view for describing a plurality of areas set on thelight-incident surface of the dust-proof cover in the first embodiment.

FIG. 11 is a transverse cross-sectional view of a projector of relatedart.

FIG. 12 is a plan view for describing a plurality of areas set in adust-proof cover according to a first variation of the first embodiment.

FIG. 13 is a plan view for describing a plurality of areas set in adust-proof cover according to a second variation of the firstembodiment.

FIG. 14 is a plan view for describing a plurality of areas set in adust-proof cover according to a third variation of the first embodiment.

FIG. 15 is a perspective view showing how a projector according to asecond embodiment is used.

FIG. 16 is a transverse cross-sectional view showing a schematicconfiguration of the interior of the projector in the second embodiment.

FIG. 17 describes a schematic configuration of a projection system inthe second embodiment.

FIG. 18 shows a schematic configuration of an image formation opticalunit in the second embodiment.

FIG. 19 is an exterior perspective view of a dust-proof cover in thesecond embodiment.

FIG. 20 is a front view of the dust-proof cover in the secondembodiment.

FIG. 21 shows the relationship between the reflectance and the angle ofincidence of projection light incident on the dust-proof cover in thesecond embodiment.

FIG. 22 shows the reflectance at which light to be projected on a screenprojection surface is reflected off a dust-proof cover in the secondembodiment when the dust-proof cover has an entirely flat singlelight-incident surface and the projector using the dust-proof coverdisplays an image.

FIG. 23 is an exterior perspective view of a projector according to afirst variation of the second embodiment.

FIG. 24 is an exterior perspective view of a projector according to athird embodiment of the invention.

FIG. 25 is a partial enlarged view of a reflection optical unit providedin a projection system of the projector in the third embodiment.

FIG. 26 shows an exterior perspective view of a dust-proof cover in thethird embodiment.

FIG. 27 is a front view of the dust-proof cover in the third embodiment.

FIG. 28 is a transverse cross-sectional view but does not show theinterior configuration of the projector in the third embodiment.

FIG. 29 is an exterior perspective view of a projector according to afirst variation of the third embodiment.

FIG. 30 is an exterior perspective view of a projector according to asecond variation of the third embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the invention will be described below in detail withreference to the drawings.

First Embodiment

FIG. 1 is a perspective view showing how a projector according to afirst embodiment of the invention is used. FIG. 2 is a transversecross-sectional view showing a schematic configuration of the interiorof the projector. FIG. 3 is a front cross-sectional view but does notshow the interior configuration of the projector. The projector 1 is afront projection-type projector that projects projection light on ascreen 10 to display an image. A viewer observes the image displayed onthe screen 10. The projector 1 is a proximity projection-type projectorthat is positioned in the vicinity of the screen 10 and projectswide-angle projection light on the screen 10 to display an image.

The screen 10 is a reflective projection plate and diffuses and reflectsthe light incident on a front-side screen projection surface(illuminated surface) 10 a to display an image. The axis along a normalto the screen projection surface 10 a is called a Z axis. The axesperpendicular to the Z axis and intersecting each other at right anglesare called an X axis and a Y axis.

The projector 1 generally includes a housing 2, a dust-proof cover(cover portion) 4, and a projection unit 6. The projection unit 6 ishoused in the housing 2. Among the components described above, theprojection unit 6 will first be described. The projection unit 6includes a projection system 50 and an image formation optical unit 60.

The projection system 50 enlarges and projects an image on an objectplane OS1 onto the screen projection surface 10 a of the screen 10. Theprojection system 50 includes a refraction optical unit 20 and areflection optical unit (wide-angle light forming reflector) 30. Therefraction optical unit 20 is formed of a plurality of lenses, and thereflection optical unit 30 has at least one concave reflection surface.

FIG. 4 describes a schematic configuration of the projection system 50.The refraction optical unit 20 is formed of a plurality of refractivelenses disposed below the screen 10 shown in FIG. 2 and along an opticalaxis OA1 extending in the direction perpendicular to the screenprojection surface 10 a. The lenses are arranged between the objectplane OS1 and the reflection optical unit 30. Each of the lenses hasrotational symmetry about the optical axis OA1. Alternatively, all orpart of the lenses may have rotational asymmetry. The arrangement of thelenses is adjusted in such a way that projection onto the screen 10 canbe optimized in consideration of the shapes and arrangements of thereflection optical unit 30 and other components. The optical axis OA1does not necessarily extend in the direction perpendicular to the screenprojection surface 10 a. Further, all or part of the lenses may notshare a single optical axis.

Each object point on the object plane OS1 emits a light flux thatuniformly diverges from the principal ray, which is perpendicular to theobject plane OS1 and parallel to the optical axis OA1. Each of the lightfluxes emitted from the object plane OS1 passes through the refractionoptical unit 20, is reflected off the reflection optical unit 30provided below the optical axis OA1 and converted into radial projectionlight, and is projected on the screen 10.

The reflection optical unit 30 is formed of a single curved mirror 31.The curved mirror 31 is a concave reflection mirror formed of a surfacerotationally symmetric about the optical axis OA1. The curved mirror 31has an aspheric reflective optical surface 31 a below the optical axisOA1, that is, on the opposite side of the optical axis OA1 with respectto the screen 10, and reflects the light fluxes having passed throughthe refraction optical unit 20 toward the screen projection surface 10 aof the screen 10. The light fluxes having passed through the refractionoptical unit 20 are reflected off the curved mirror 31, which is aconcave reflection mirror, and first converge but then diverge. That is,the curved mirror 31 serves to form wide-angle projection light. Whilethe projection system 50 is formed of the refraction optical unit 20 andthe reflection optical unit 30 in the above description, the projectionsystem 50 may alternatively be formed only of a refraction optical unitor a reflection optical unit having a power.

The image formation optical unit 60 will next be described. FIG. 5 showsa schematic configuration of the image formation optical unit 60. An arctube 70 is a light source that emits light containing red (R) light,green (G) light, and blue (B) light. The arc tube 70 is, for example, anultrahigh-pressure mercury lamp.

A first integrator lens 71 and a second integrator lens 72 are arrays ofa plurality of lens elements. The first integrator lens 71 divides thelight flux from the arc tube 70 into a plurality of sub-light fluxes.Each of the lens elements in the first integrator lens 71 focuses thelight flux from the arc tube 70 in the vicinity of the correspondinglens element in the second integrator lens 72. Each of the lens elementsin the second integrator lens 72 forms the image of the correspondinglens element in the first integrator lens 71 on spatial lightmodulators.

The light having passed through the two integrator lenses 71 and 72 isconverted by a polarization conversion element 73 into light linearlypolarized in a specific oscillation direction. A superimposing lens 74superimposes the images of the lens elements in the first integratorlens 71 on the spatial light modulators. The first integrator lens 71,the second integrator lens 72, and the superimposing lens 74 make theintensity distribution of the light from the arc tube 70 uniform on thespatial light modulators. The light having passed through thesuperimposing lens 74 is incident on a first dichroic mirror 75. Thefirst dichroic mirror 75 reflects the R light, whereas transmitting theG light and the B light. The optical path of the R light reflected offthe first dichroic mirror 75 is folded by the first dichroic mirror 75and a reflection mirror 76, and the R light is incident on a field lensfor R light 77R. The field lens for R light 77R parallelizes the R lightreflected off the reflection mirror 76 and directs the R light to aspatial light modulator for R light 14R.

The spatial light modulator for R light 14R modulates the R light inaccordance with an image signal. The R light modulated by the spatiallight modulator for R light 14R is incident on a cross dichroic prism80, which is a light combining system.

The G light and the B light having passed through the first dichroicmirror 75 are incident on a second dichroic mirror 81. The seconddichroic mirror 81 reflects the G light, whereas transmitting the Blight. The optical path of the G light reflected off the second dichroicmirror 81 is folded by the second dichroic mirror 81, and the G light isincident on a field lens for G light 77G. The field lens for G light 77Gparallelizes the G light reflected off the second dichroic mirror 81 anddirects the G light to a spatial light modulator for G light 14G. Thespatial light modulator for G light 14G modulates the G light inaccordance with the image signal. The G light modulated by the spatiallight modulator for G light 14G is incident on a surface of the crossdichroic prism 80 that differs from the surface on which the R light isincident.

The B light having passed through the second dichroic mirror 81 passesthrough a relay lens 82, and the optical path of the B light is foldedwhen the B light is reflected off a reflection mirror 83. The B lightreflected off the reflection mirror 83 passes through a relay lens 84,and the optical path of the B light is folded when the B light isreflected off a reflection mirror 85. The B light is then incident on afield lens for B light 77B. Since the optical path of the B light islonger than those of the R light and the G light, the relay systemformed of the relay lenses 82 and 84 is provided in the optical path ofthe B light in order to make the illumination magnifications in thespatial light modulators equal for all the color light beams.

The field lens for B light 77B parallelizes the B light reflected offthe reflection mirror 85 and directs the B light to a spatial lightmodulator for B light 14B. The spatial light modulator for B light 14Bmodulates the B light in accordance with the image signal. The B lightmodulated by the spatial light modulator for B light 14B is incident ona surface of the cross dichroic prism 80 that differs from the surfaceson which the R light and the G light are incident.

The cross dichroic prism 80 has two dichroic layers 86 and 87 disposedin such a way that they intersect each other at substantially rightangles. The first dichroic layer 86 reflects the R light, whereastransmitting the G light and the B light. The second dichroic layer 87reflects the B light, whereas transmitting the R light and the G light.The cross dichroic prism 80 combines the R light, the G light, and the Blight, which are incident from the directions different from oneanother, and outputs the combined light toward the projection system 50.The image light having exited from the cross dichroic prism 80 isprojected after passing through the refraction optical unit 20 and othercomponents in the projection system 50.

The housing 2 and the dust-proof cover 4 will next be described. Thehousing 2 houses the projection system 50 and the image formationoptical unit 60. The housing 2 has an opening 2 a in a top portion 2 b,and the opening 2 a allows the projection light projected from theprojection system 50 to exit outward.

The dust-proof cover 4 is provided in the housing 2 to block the opening2 a. The projection unit 6 in the housing is protected from dust anddirt by blocking the opening 2 a with the dust-proof cover 4. Blockingthe opening 2 a further not only prevents, for example, foreign matterfrom entering the housing but also prevents the projection unit 6 frombeing destroyed or scratched. The dust-proof cover 4 is made of alight-transmissive material, for example, glass and plastics. Since thedust-proof cover 4 is made of a light-transmissive material, theprojection light projected from the projection unit 6 can reach thescreen 10 through the dust-proof cover 4. Further, the dust-proof cover4 has a substantially uniform thickness.

FIG. 6 is a plan view of the dust-proof cover 4. The dust-proof cover 4has a substantially rectangular shape in the plan view. FIG. 6 showscontour lines indicating the actual angle of incidence of the projectionlight that impinges on the light-incident surface of the dust-proofcover 4. The angle of incidence of the projection light that impinges onthe light-incident surface of the dust-proof cover 4 ranges widely fromapproximately 25 degrees to approximately 85 degrees. The contour linescorresponding to 40 degrees and smaller are omitted because the spacingstherebetween are narrow. The angle of incidence used herein is the anglebetween a normal to the light-incident surface in the position where aprojection light ray of interest is incident and the projection lightray.

Part of the light incident on the dust-proof cover 4 is reflected offthe light-incident surface thereof and disadvantageously lost. The ratioof the amount of light reflected off the dust-proof cover 4 to the totalamount of light incident thereon, that is, the reflectance, isdetermined by the angle of incidence of the projection light.

FIG. 7 shows the relationship between the reflectance and the angle ofincidence of the projection light at a predetermined point on a flatglass member that can be used to form the dust-proof cover 4. As shownin FIG. 7, the reflectance increases as the angle of incidenceincreases. The reflectance increases by approximately 20% when the angleof incidence increases from 0 to 70 degrees, and increases by another20% when the angle of incidence increases from 70 to 80 degrees. Thatis, when the angle of incidence changes from 0 to 70 degrees, the amountof projection light that reaches the screen decreases by approximately20%, and when the angle of incidence changes from 70 to 80 degrees, theamount of projection light that reaches the screen decreases by another20%.

FIG. 8 shows the reflectance at which the light to be projected on thescreen projection surface 10 a is reflected off the dust-proof cover 4when a single anti-reflection film is formed on the entirelight-incident surface of the dust-proof cover and the projector usingthe dust-proof cover displays an image. In general, when the amount oflight decreases 10% or more, the viewer senses decrease in brightness.As shown in FIG. 8, using the dust-proof cover having a singleanti-reflection film formed on the entire light-incident surface leadsto decrease in the amount of light by at least 10% in lower right andleft portions of the screen projection surface 10 a, and the viewersenses that the brightness decreases in these portions.

FIG. 9 shows the relationship between the positions on the dust-proofcover 4 where projection light rays are incident and the positions onthe screen 10 where the projection light rays are projected. As shown inFIG. 9, almost all the projection light rays to be projected on thescreen 10 are incident on a central portion of the dust-proof cover 4.On the other hand, projection light rays to be projected in a lowerportion of the screen (points u to y) are incident on a peripheralportion of the dust-proof cover 4.

FIG. 10 is a plan view for describing a plurality of areas set in thedust-proof cover 4. A plurality of areas is set in the dust-proof cover4 relative to the projection unit 6. In other words, the plurality ofareas is set based on which portion of the projection light from theprojection unit 6 is incident or how the projection light from theprojection unit 6 is incident. Specifically, a first area (referencearea) 15 a including an area where the projection light is incident atan angle of incidence ranging from 25 to 70 degrees is set on thelight-incident surface of the dust-proof cover 4. A second area 15 bincluding an area where the projection light is incident at an angle ofincidence ranging from 70 to 80 degrees is set outside the first area 15a. Further, third areas 15 c including areas where the projection lightis incident at an angle of incidence equal to or greater than 80 degreesare set outside the second area 15 b.

The first area 15 a is provided with an anti-reflection film (ARcoating) showing an anti-reflection effect on the projection lightincident at an angle of incidence ranging from 25 to 70 degrees. Thesecond area 15 b is provided with an anti-reflection film showing ananti-reflection effect on the projection light incident at an angle ofincidence ranging from 70 to 80 degrees. Each of the third areas 15 c isprovided with an anti-reflection film showing an anti-reflection effecton the projection light incident at an angle of incidence equal to orgreater than 80 degrees. That is, a process of preventing the reflectionof the projection light incident at a larger angle of incidence isperformed on an area spaced further apart from the first area 15 a.

FIG. 11 is a transverse cross-sectional view of a projector 101 ofrelated art. The projector 101 of related art is a proximityprojection-type projector, like the projector 1 of the first embodiment.In a proximity projection-type projector, the projection light isinclined toward the screen 10 in the YZ plane in order to project thelight toward the screen 10. In the projector 101 of related art, toprevent the angle of incidence of the light incident on a dust-proofcover 104 from increasing due to the inclined projection light, thedust-proof cover 104 is provided in such a way that the light-exitingsurface thereof is inclined and oriented toward the screen 10. As shownin FIG. 3, however, the projection light from the projector is incidentat a variety of angles of incidence also in the XY plane. Therefore,inclining the dust-proof cover 104 to compensate the change in the angleof incidence only in the YZ plane cannot effectively reduce the loss dueto the reflection.

In the first embodiment, since a plurality of areas is set on thelight-incident surface of the dust-proof cover 4 and each of the areasis provided with an anti-reflection film having an anti-reflectioneffect according to the actual angle of incidence of the projectionlight, the loss due to the reflection off the light-incident surface andhence decrease in image brightness can be reduced. Further, the cost canbe reduced as compared to a case where a multilayer coating film isformed on the entire light-incident surface of the dust-proof cover 4 toachieve an anti-reflection capability across a wide range of angle ofincidence. In the first embodiment, the areas are separated in terms ofthe angle of incidence in such a way that a new area is set when thereflectance increases by approximately 20%, as shown in FIG. 7. Theareas are not necessarily set in the way described above, but the sizeof each of the areas may be smaller. An example of the anti-reflectionfilm for preventing the reflection off the light-incident surface may bea dielectric multilayer coating. As another example of theanti-reflection process, a sub-wavelength structure or any other minutestructure may be provided on the light-incident surface to prevent thereflection off the light-incident surface. That is, the anti-reflectionprocess is not limited to the use of an anti-reflection film but may beany process that achieves an angle-dependent, anti-reflection effectacross the range of angle of incidence of the projection light incidenton each of the divided areas.

The dust-proof cover 4, which has a uniform thickness thereacross, canbe a member having no optical power. When the dust-proof cover 4 has nooptical power, a slight positional error in a process of attaching thedust-proof cover 4 does not greatly affect the image quality. Thisallows the projector 1 to be assembled at a lower cost and furtherallows the dust-proof cover 4 to be readily exchanged, whereby ease ofmaintenance can be improved.

While the first embodiment has been described with reference to a frontprojection-type projector, the projector in the first embodiment may ofcourse be a rear projection-type projector. The first embodiment mayalso be applied to a scanning projector that scans a laser beam on ascreen to display an image. For example, when the screen has a huge sizeor an image is projected from the projector located close to the screen,the laser beam is scanned over a large angle, and the laser beam isincident on the dust-proof cover at large angles of incidence. In thiscase, using the dust-proof cover described in the first embodiment canprevent decrease in image brightness. Further, while the firstembodiment has been described with reference to a projector using adust-proof cover having undergone an anti-reflection process, thedust-proof cover may be used with a camera including a wide-angle lensto prevent light reflection, and the same advantageous effect on acaptured image can be provided as in the first embodiment. An example ofthe camera including a wide-angle lens may be a security camera.

FIG. 12 is a plan view for describing how to set areas of a dust-proofcover 204 according to a first variation of the first embodiment. In thefirst variation, the light-incident surface of the dust-proof cover 204is divided into three areas in the longitudinal direction. Among thethree areas, the central area in the longitudinal direction is set as afirst area (reference area) 16 a including an area where the projectionlight is incident at an angle of incidence ranging from 25 to 75degrees. The areas on both sides of the first area 16 a are set assecond areas 16 b, each of which including an area where the projectionlight is incident at an angle of incidence equal to or greater than 75degrees.

The first area 16 a is provided with an anti-reflection film having ananti-reflection effect on the projection light incident at an angle ofincidence ranging from 25 to 75 degrees. Each of the second areas 16 bis provided with an anti-reflection film having an anti-reflectioneffect on the projection light incident at an angle of incidence equalto or greater than 75 degrees. That is, a process of preventing thereflection of the projection light incident at a larger angle ofincidence is performed on an area spaced further apart from the firstarea 16 a.

As shown in FIG. 8, the light projected on lower right and left portionssuffers from significant reduction in the amount of light projected onthe screen 10. As shown in FIG. 9, the light projected on the lowerright and left portions (points u, v, x, and y) of the screen 10 isincident on the areas set as the second areas 16 b of the dust-proofcover 204, whereas most of the light projected on the remaining portionof the screen 10 (the light that does not suffer from significantreduction in the amount of light) is incident on the area set as thefirst area 16 a of the dust-proof cover 204.

Setting small areas, like the dust-proof cover 4 described in the firstembodiment, allows the amount of projection light that reaches thescreen 10 to be increased. Even when the light-incident surface of thedust-proof cover 204 is divided into three areas in the longitudinaldirection in the first variation, the viewer will still not sense thatthe amount of light decreases. As compared to the case where smallerareas are set, the anti-reflection film and other components are readilyprocessed and formed, whereby the cost can be reduced.

FIG. 13 is a plan view for describing how to set areas of a dust-proofcover 304 according to a second variation of the first embodiment. Inthe second variation, the light-incident surface of the dust-proof cover304 is divided into three areas in the longitudinal direction, and theareas overlap with each other. Among the three areas, the central areain the longitudinal direction is set as a first area (reference area) 17a including an area where the projection light is incident at an angleof incidence ranging from 25 to 75 degrees. The areas on both sides ofthe first area 17 a are set as second areas 17 b, each of whichincluding an area where the projection light is incident at an angle ofincidence equal to or greater than 75 degrees.

The first area 17 a is provided with an anti-reflection film having ananti-reflection effect on the projection light incident at an angle ofincidence ranging from 25 to 75 degrees. Each of the second areas 17 bis provided with an anti-reflection film having an anti-reflectioneffect on the projection light incident at an angle of incidence equalto or greater than 75 degrees. That is, a process of preventing thereflection of the projection light incident at a larger angle ofincidence is performed on an area spaced further apart from the firstarea 17 a.

The first area 17 a and each of the second areas 17 b, that is, theadjacent areas, overlap with each other (the hatched portions in FIG.13). The overlaps are provided with the anti-reflection film. Formingthe overlaps allows the brightness of an image displayed on the screen10 to change smoothly and hence prevents the viewer from recognizing theboundary between the areas that overlap with each other.

FIG. 14 is a plan view for describing how to set areas of a dust-proofcover 404 according to a third variation of the first embodiment. In thethird variation, the light-incident surface of the dust-proof cover 404is divided into two areas in the short-side direction. One of the twoareas is set as a first area (reference area) 18 a including an areawhere the projection light is incident at an angle of incidence rangingfrom 25 to 65 degrees. The area other than the first area 18 a is set asa second area 18 b including an area where the projection light isincident at an angle of incidence equal to or greater than 70 degrees.

As shown in FIG. 8, the light projected on lower right and left portionssuffers from significant reduction in the amount of light projected onthe screen 10. As shown in FIG. 9, the light projected on the lowerright and left portions (points u, v, x, and y) of the screen 10 isincident on the area set as the second area 18 b of the dust-proof cover404, whereas most of the light projected on the remaining portion of thescreen 10 (the light that does not suffer from significant reduction inthe amount of light) is incident on the area set as the first area 18 aof the dust-proof cover 404.

Setting small areas, like the dust-proof cover 4 described in the firstembodiment, allows the amount of projection light that reaches thescreen 10 to be increased. Even when the light-incident surface of thedust-proof cover 404 is divided into two areas in the short-sidedirection in the third variation, the viewer will still not sense thatthe amount of light decreases. As compared to the case where smallerareas are set, the anti-reflection film and other components are readilyprocessed and formed, whereby the cost can be reduced.

To form wide-angle projection light, the curved mirror 31 is notnecessarily used. For example, a shift optical system may be used toform wide-angle projection light.

Second Embodiment

FIG. 15 is a perspective view showing how a projector according to asecond embodiment of the invention is used. FIG. 16 is a transversecross-sectional view showing a schematic configuration of the interiorof the projector. The projector 501 is a front projection-type projectorthat projects projection light on a screen to display an image. A viewerobserves the image displayed on the screen. The projector 501 is aproximity projection-type projector that is positioned in the vicinityof a screen 510 and projects wide-angle projection light on the screen510 to display an image.

The screen 510 is a reflective projection plate and diffuses andreflects the light incident on a front-side screen projection surface(illuminated surface) 510 a to display an image. The axis along a normalto the screen projection surface 510 a is called a Z axis. The axesperpendicular to the Z axis and intersecting each other at right anglesare called an X axis and a Y axis.

The projector 501 generally includes a housing 502, a dust-proof cover(cover portion) 504, and a projection unit 506. The projection unit 506is housed in the housing 502. Among the components described above, theprojection unit 506 will first be described. The projection unit 506includes a projection system 550 and an image formation optical unit560.

The projection system 550 enlarges and projects an image on an objectplane OS2 onto the screen projection surface 510 a of the screen 510.The projection system 550 includes a refraction optical unit 520 and areflection optical unit (wide-angle light forming reflector) 530. Therefraction optical unit 520 is formed of a plurality of lenses, and thereflection optical unit 530 has at least one concave reflection surface.

FIG. 17 describes a schematic configuration of the projection system550. The refraction optical unit 520 is formed of a plurality ofrefractive lenses disposed below the screen 510 shown in FIG. 16 andalong an optical axis OA2 extending in the direction perpendicular tothe screen projection surface 510 a. The lenses are arranged between theobject plane OS2 and the reflection optical unit 530. Each of the lenseshas rotational symmetry about the optical axis OA2. Alternatively, allor part of the lenses may have rotational asymmetry. The arrangement ofthe lenses is adjusted in such a way that projection onto the screen 510can be optimized in consideration of the shapes and arrangements of thereflection optical unit 530 and other components. The optical axis OA2does not necessarily extend in the direction perpendicular to the screenprojection surface 510 a. Further, all or part of the lenses may notshare a single optical axis.

Each object point on the object plane OS2 emits a light flux thatuniformly diverges from the principal ray, which is perpendicular to theobject plane OS2 and parallel to the optical axis OA2. Each of the lightfluxes emitted from the object plane OS2 passes through the refractionoptical unit 520, is reflected off the reflection optical unit 530provided below the optical axis OA2 and converted into radial projectionlight, and is projected on the screen 510.

The reflection optical unit 530 is formed of a single curved mirror 531.The curved mirror 531 is a concave reflection mirror formed of a surfacerotationally symmetric about the optical axis OA2. The curved mirror 531has an aspheric reflective optical surface 531 a below the optical axisOA2, that is, on the opposite side of the optical axis OA2 with respectto the screen 510, and reflects the light fluxes having passed throughthe refraction optical unit 520 toward the screen projection surface 510a of the screen 510. The light fluxes having passed through therefraction optical unit 520 are reflected off the curved mirror 531,which is a concave reflection mirror, and first converge but thendiverge. That is, the curved mirror 531 serves to form wide-angleprojection light. While the projection system 550 is formed of therefraction optical unit 520 and the reflection optical unit 530 in theabove description, the projection system 550 may alternatively be formedonly of a refraction optical unit or a reflection optical unit having apower.

The image formation optical unit 560 will next be described. FIG. 18shows a schematic configuration of the image formation optical unit 560.An arc tube 570 is a light source that emits light containing red (R)light, green (G) light, and blue (B) light. The arc tube 70 is, forexample, an ultrahigh-pressure mercury lamp.

A first integrator lens 571 and a second integrator lens 572 are arraysof a plurality of lens elements. The first integrator lens 571 dividesthe light flux from the arc tube 570 into a plurality of sub-lightfluxes. Each of the lens elements in the first integrator lens 571focuses the light flux from the arc tube 570 in the vicinity of thecorresponding lens element in the second integrator lens 572. Each ofthe lens elements in the second integrator lens 572 forms the image ofthe corresponding lens element in the first integrator lens 571 onspatial light modulators.

The light having passed through the two integrator lenses 571 and 572 isconverted by a polarization conversion element 573 into light linearlypolarized in a specific oscillation direction. A superimposing lens 574superimposes the images of the lens elements in the first integratorlens 571 on the spatial light modulators. The first integrator lens 571,the second integrator lens 572, and the superimposing lens 574 make theintensity distribution of the light from the arc tube 570 uniform on thespatial light modulators. The light having passed through thesuperimposing lens 574 is incident on a first dichroic mirror 575. Thefirst dichroic mirror 575 reflects the R light, whereas transmitting theG light and the B light. The optical path of the R light reflected offthe first dichroic mirror 575 is folded by the first dichroic mirror 575and a reflection mirror 576, and the R light is incident on a field lensfor R light 577R. The field lens for R light 577R parallelizes the Rlight reflected off the reflection mirror 576 and directs the R light toa spatial light modulator for R light 514R.

The spatial light modulator for R light 514R modulates the R light inaccordance with an image signal. The R light modulated by the spatiallight modulator for R light 514R is incident on a cross dichroic prism580, which is a light combining system.

The G light and the B light having passed through the first dichroicmirror 575 are incident on a second dichroic mirror 581. The seconddichroic mirror 581 reflects the G light, whereas transmitting the Blight. The optical path of the G light reflected off the second dichroicmirror 581 is folded by the second dichroic mirror 581, and the G lightis incident on a field lens for G light 577G. The field lens for G light577G parallelizes the G light reflected off the second dichroic mirror581 and directs the G light to a spatial light modulator for G light514G. The spatial light modulator for G light 514G modulates the G lightin accordance with the image signal. The G light modulated by thespatial light modulator for G light 514G is incident on a surface of thecross dichroic prism 580 that differs from the surface on which the Rlight is incident.

The B light having passed through the second dichroic mirror 581 passesthrough a relay lens 582, and the optical path of the B light is foldedwhen the B light is reflected off a reflection mirror 583. The B lightreflected off the reflection mirror 583 passes through a relay lens 584,and the optical path of the B light is folded when the B light isreflected off a reflection mirror 585. The B light is then incident on afield lens for B light 577B. Since the optical path of the B light islonger than those of the R light and the G light, the relay systemformed of the relay lenses 582 and 584 is provided in the optical pathof the B light in order to make the illumination magnifications in thespatial light modulators equal for all the color light beams.

The field lens for B light 577B parallelizes the B light reflected offthe reflection mirror 585 and directs the B light to a spatial lightmodulator for B light 514B. The spatial light modulator for B light 514Bmodulates the B light in accordance with the image signal. The B lightmodulated by the spatial light modulator for B light 514B is incident ona surface of the cross dichroic prism 580 that differs from the surfaceson which the R light and the G light are incident.

The cross dichroic prism 580 has two dichroic layers 586 and 587disposed in such a way that they intersect each other at substantiallyright angles. The first dichroic layer 586 reflects the R light, whereastransmitting the G light and the B light. The second dichroic layer 587reflects the B light whereas transmitting the R light and the G light.The cross dichroic prism 580 combines the R light, the G light, and theB light, which are incident from the directions different from oneanother, and outputs the combined light toward the projection system.550. The image light having exited from the cross dichroic prism 580 isprojected after passing through the refraction optical unit 520 andother components in the projection system 550.

The housing 502 and the dust-proof cover 504 will next be described. Thehousing 502 houses the projection system 550 and the image formationoptical unit 560. The housing 502 has an opening 502 a in a top portion502 b, and the opening 502 a allows the projection light projected fromthe projection system 550 to exit outward.

The dust-proof cover 504 is provided in the housing 502 to block theopening 502 a. The projection unit 506 in the housing 502 is protectedfrom dust and dirt by blocking the opening 502 a with the dust-proofcover 504. Blocking the opening 502 a further not only prevents, forexample, foreign matter from entering the housing 502 but also preventsthe projection unit 506 from being destroyed or scratched. Thedust-proof cover 504 is made of a light-transmissive material, forexample, glass and plastics. Since the dust-proof cover 504 is made of alight-transmissive material, the projection light projected from theprojection unit 506 can reach the screen 510 through the dust-proofcover 504.

FIG. 19 is an exterior perspective view of the dust-proof cover 504.FIG. 20 is a front view of the dust-proof cover 504. As shown in FIGS.19 and 20, the dust-proof cover 504 has a substantially uniformthickness. The dust-proof cover 504 has a central portion 504 a andperipheral portions 504 b adjacent to the central portion 504 a. Thatis, the dust-proof cover 504 is formed of two types of areas, thecentral portion 504 a and the peripheral portions 504 b. The centralportion 504 a and the peripheral portions 504 b are positioneddifferently from each other relative to the projection unit 506. Inother words, the central portion 504 a and the peripheral portions 504 bdiffer from each other in terms of which portion of the projection lightfrom the projection unit 506 is incident or how the projection lightfrom the projection unit 506 is incident. The central light of theprojection light is incident on the central portion 504 a, and theperipheral light of the projection light is incident on the peripheralportions 504 b. Each of the central portion 504 a and the peripheralportions 504 b is formed of a flat member, and each of the peripheralportions 504 b is inclined to the central portion 504 a and bent towardthe side on which the projection light is incident. As shown in FIG. 20,the central portion 504 a has a substantially rectangular shape, and theperipheral portions 504 b are connected only to a pair of sides of thecentral portion 504 a that face each other. Therefore, the dust-proofcover 504 can be manufactured only by bending both sides of a glassplate or a plastic plate having an entirely flat structure, whereby themanufacturing cost can be reduced.

Part of the light incident on the dust-proof cover 504 is reflected offthe light-incident surface thereof and disadvantageously lost. The ratioof the amount of light reflected off the dust-proof cover 504 to thetotal amount of light incident thereon, that is, the reflectance, isdetermined by the angle of incidence of the projection light. The angleof incidence used herein is the angle between a normal to thelight-incident surface in the position where a projection light ray ofinterest is incident and the projection light ray.

FIG. 21 shows the relationship between the reflectance and the angle ofincidence of the projection light at a predetermined point on a flatglass member that can be used to form the dust-proof cover 504. As shownin FIG. 21, the reflectance increases as the angle of incidenceincreases. In FIG. 20, the dashed line indicates a dust-proof cover 505having no peripheral bent portions but having an entirely flat singlelight-incident surface. The dust-proof cover 505 having an entirely flatsingle light-incident surface shows a large reflectance value inperipheral portions 505 b where the angle of incidence α1 increases.That is, the dust-proof cover 505 having an entirely flat singlelight-incident surface is disadvantageous in that most of the lightincident on the peripheral portions 505 b is reflected and the imageportion formed by the light having passed through the peripheralportions 505 b has reduced brightness.

FIG. 22 shows the reflectance at which the light to be projected on thescreen projection surface 510 a is reflected off the dust-proof cover505 when the dust-proof cover 505 has an entirely flat singlelight-incident surface and the projector using the dust-proof cover 505displays an image. In general, when the amount of light decreases 10% ormore, the viewer senses decrease in brightness. As clearly shown in FIG.22, using the dust-proof cover 505 having an entirely flat singlelight-incident surface leads to decrease in the amount of light by atleast 10% in lower right and left portions of the screen projectionsurface 510 a, and the viewer senses that the brightness decreases inthese portions.

In contrast, since the dust-proof cover 504 of the second embodiment hasthe bent peripheral portions 504 b, the angle of incidence a2 and hencethe reflectance will not greatly increase. Therefore, the dust-proofcover 504 of the second embodiment does not likely cause the viewer tosense decrease in brightness in the image portion formed by the lighthaving passed through the peripheral portions 504 b.

The dust-proof cover 504, which has a uniform thickness thereacross, hasno optical power. When the dust-proof cover 504 has no optical power, aslight positional error in a process of attaching the dust-proof cover504 does not greatly affect the image quality. This allows the projector501 to be assembled at a lower cost and further allows the dust-proofcover 504 to be readily exchanged, whereby ease of maintenance can beimproved.

Further, since each of the central portion 504 a and the peripheralportions 504 b of the dust-proof cover 504 is formed of a flat member,the manufacturing cost can be reduced compared to a case where each ofthe central portion 504 a and the peripheral portions 504 b is formed ofa curved member.

In the second embodiment, the dust-proof cover 504 is bent so that thereflectance at which the projection light is reflected decreases. Ananti-reflection film (AR coating) may be formed on the light-incidentsurface of the dust-proof cover 504 to further reduce the reflectance.

On the other hand, since the dust-proof cover 504 is bent along theboundaries between the central portion 504 a and each of the peripheralportions 504 b, the light having passed through the boundaries may bedistorted in some cases. To correct the distortion, the spatial lightmodulators 514R, 514G, and 514B may be used to correct in advance thelight passing through the boundaries.

While the second embodiment has been described with reference to a frontprojection-type projector, the projector in the second embodiment may ofcourse be a rear projection-type projector. The second embodiment mayalso be applied to a scanning projector that scans a laser beam on ascreen to display an image. For example, when the screen has a huge sizeor an image is projected from the projector located close to the screen,the laser beam is scanned over a large angle. In this case, using thedust-proof cover described in the second embodiment can prevent decreasein image brightness. Further, while the second embodiment has beendescribed with reference to a projector including a bent dust-proofcover, the dust-proof cover may be used with a camera including awide-angle lens to reduce the angle of incidence of the light incidenton the dust-proof cover, and the same advantageous effect on a capturedimage can be provided as in the second embodiment. An example of thecamera including a wide-angle lens may be a security camera.

FIG. 23 is an exterior perspective view of the projector 501 accordingto a first variation of the second embodiment. The components that arethe same as those described above have the same reference characters,and no redundant description thereof will be made. As shown in FIG. 23,the dust-proof cover 504 may be provided in a side portion 502 c of thehousing 502.

Providing the dust-proof cover 504 in the side portion 502 c of thehousing 502 allows the invention to be applied to not only a proximityprojection-type projector but also other types of projector. Forexample, a projector that projects projection light from a position infront a screen but spaced far apart therefrom also needs to project theprojection light over a wide range when the screen has a large width. Inthis case, the angle of incidence of the projection light incident onthe cover portion may increase. Using the bent dust-proof cover 504reduces the angle of incidence of the projection light projected acrossthe wide range, whereby the loss due to the reflection and hencedecrease in image brightness can be reduced. The side portion 502 c usedherein is the integrated portion formed of the four surfaces of thehousing 502 except the top portion 502 b and the bottom portion (notshown).

Third Embodiment

FIG. 24 is an exterior perspective view of a projector 601 according toa third embodiment of the invention. The components that are the same asthose in the second embodiment have the same reference characters, andno redundant description thereof will be made. The projector 601according to the third embodiment is characterized in that the surfaceof a central portion 604 a of a dust-proof cover 604 through which theprojection light exits is inclined toward the screen 510. The projector601 is further characterized in that peripheral portions 604 b of thedust-proof cover 604 are bent and inclined to the central portion 604 aby 90 degrees.

FIG. 25 is a partial enlarged view of a reflection optical unit(wide-angle light forming reflector) 630 provided in the projectionsystem 550 of the projector 601. The reflection optical unit 630includes a curved mirror 631. While the curved mirror 531 described inthe second embodiment has a concave shape, the curved mirror 631 in thethird embodiment has a convex shape.

Since the curved mirror 631 has a convex shape, the light reflected offthe curved mirror 631 does not converge but diverge. That is, the lightreflected off the curved mirror 631 spreads across a wide range even ina position that is not greatly spaced apart from the curved mirror 631as compared to the case where the light is reflected off the concavecurved mirror 531. When the curved mirror 631 of the third embodiment isused, it is necessary to shift the projection light in the refractionoptical unit 520 to a level above the optical axis OA2, but nodescription of the configuration of lenses for shifting the projectionlight and other features will be made.

FIG. 26 is an exterior perspective view of the dust-proof cover 604 usedin the projector 601. FIG. 27 is a front view of the dust-proof cover604. The peripheral portions 604 b of the dust-proof cover 604 are bentand inclined to the central portion 604 a by approximately 90 degrees.In FIG. 27, the dashed line indicates a dust-proof cover 605 having noperipheral bent portions but having an entirely flat singlelight-incident surface. As clearly shown in FIG. 27, bending theperipheral portions 604 b by approximately 90 degrees allows theprojection light spreading across a wide range to be transmitted to thedust-proof cover 604 configured in a more compact manner than that ofthe dust-proof cover 605 having an entirely flat single light-incidentsurface. Further, since the peripheral portions 604 b are bent, the lossof light due to the reflection and hence the decrease in imagebrightness can be reduced.

The inclination of the central portion 604 a of the dust-proof cover 604will next be described. FIG. 28 is a transverse cross-sectional view ofthe projector 601 but does not show the interior configuration thereof.The dust-proof cover 604 is attached to the housing 502 in such a waythat the surface of the central portion 604 a through which theprojection light exits faces the screen 510.

As described above, bending the peripheral portions 604 b of thedust-proof cover 604 prevents the decrease in image brightness due tothe fact that the angle of incidence spreads across a range in the XYplane. Further, since the dust-proof cover is inclined in the thirdembodiment so that the surface of the central portion 604 a throughwhich the projection light exits faces the screen 510, the fact that theangle of incidence spreads across a range in the YZ plane will not be aproblem. In particular, since a proximity projection-type projector is,in general, installed below the screen 510, the projection light exitsthrough the top portion 502 b of the housing 502 and travels toward thescreen obliquely to some extent. In FIG. 28, the dashed line indicatesthe dust-proof cover 605 with the light exiting-side surface thereofuninclined. As shown in FIG. 28, the angle of incidence in the YZ planeat which the projection light is incident on the dust-proof cover 605with the light exiting-side surface thereof uninclined ranges from γ1 toγ2, resulting in a large variation. At a large angle of incidence, forexample, γ1, image brightness disadvantageously decreases. Since thedust-proof cover 604 according to the third embodiment is inclined insuch a way that the surface through which the projection light exitsfaces the screen 510, the inclination cancels the increase in the angleof incidence. That is, simply inclining the dust-proof cover 604 canprevent the decrease in image brightness. Further, even when the curvedmirror has a concave shape, inclining the dust-proof cover cancels theincrease in the angle of incidence in the YZ plane.

FIG. 29 is an exterior perspective view of the projector 601 accordingto a first variation of the third embodiment. The portions that are thesame as the components described above have the same referencecharacters, and no redundant description thereof will be made. In theprojector 601 according to the first variation, the central portion 604a of the dust-proof cover 604 is substantially parallel to the topportion 502 b of the housing 502, and the central portion 604 a is flushwith the top portion 502 a. The peripheral portions 604 b of thedust-proof cover 604 are substantially parallel to the side portion 502c of the housing 502, and the peripheral portions 604 b are flush withthe side portion 502 c.

As described above, since the central portion 604 a and the peripheralportions 604 b are substantially parallel to the top portion 502 a andthe side portion 502 c, respectively, which are part of the outersurfaces of the housing 502, the projector can be designed with noconstraint and the degree of design freedom can be increased as comparedto, for example, a case where a dome-shaped dust-proof cover isemployed. Further, since the central portion 604 a is flush with thecorresponding one of the outer surfaces of the housing 502, theprojector 601 can have a novel exterior, and the dust-proof cover 604can be integrated with the housing 502. Integrating the dust-proof cover604 with the housing 502 contributes to cost reduction because thenumber of assembly steps and the number of parts are reduced. When thedust-proof cover 604 is integrated with the housing 502, only thedust-proof cover can transmit light by forming the entire structure witha transparent member and painting the portion other than the dust-proofcover 604.

FIG. 30 is an exterior perspective view of the projector 601 accordingto a second variation of the third embodiment. The portions that are thesame as the components described above have the same referencecharacters, and no redundant description thereof will be made. In theprojector 601 of the second variation, the central portion 604 a of thedust-proof cover 604 is substantially parallel to the side portion 502 aof the housing 502, and the central portion 604 a is flush with the sideportion 502 a. The peripheral portions 604 b of the dust-proof cover 604are also substantially parallel to the side portion 502 c of the housing502, and the peripheral portions 604 b are flush with the side portion502 c.

Providing the dust-proof cover 604 in the side portion 502 c of thehousing 502 allows the invention to be applied to not only a proximityprojection-type projector but also other types of projectors. Forexample, a projector that projects projection light from a position infront a screen but spaced far apart therefrom also needs to projectwide-angle projection light when the screen has a large width.

When the convex curved mirror 631 is used to form wide-angle projectionlight, the light reflected off the curved mirror 631 spreads across awide range even in a position that is not greatly spaced apart from thecurved mirror 631. In this case as well, using the bent dust-proof cover604 can reduce the loss due to the reflection of the wide-angleprojection light and hence the decrease in image brightness. To formwide-angle projection light, the convex curved mirror 631 is notnecessarily used. For example, when a shift optical system is used toform wide-angle projection light, the projection light may spread acrossa wide range. In this case as well, using the bent dust-proof cover 604can reduce the loss due to the reflection of the projection light andhence the decrease in image brightness.

Since the central portion 604 a and the peripheral portions 604 b aresubstantially parallel to the side portion 502 c, which is part of theouter surfaces of the housing 502, the projector can be designed with noconstraint and the degree of design freedom can be increased ascompared, for example, to a case where a dome-shaped dust-proof cover isemployed. Further, since the central portion 604 a is flush with thecorresponding one of the outer surfaces of the housing 502, theprojector 601 can have a novel exterior, and the dust-proof cover 604can be integrated with the housing 502. Integrating the dust-proof cover604 with the housing 502 contributes to cost reduction because thenumber of assembly steps and the number of parts are reduced. When thedust-proof cover 604 is integrated with the housing 502, only thedust-proof cover 604 can transmit light by forming the entire structurewith a transparent member and painting the portion other than thedust-proof cover 604.

The entire disclosure of Japanese Patent Application Nos. 2008-332966,filed Dec. 26, 2008 and 2008-332967, filed Dec. 26, 2008 is expresslyincorporated by reference herein.

1. A proximity projection-type projector comprising: a housing; a dust-proof cover arranged on a top portion of the housing; a projection unit arranged within the housing, wherein the projection unit projects projection light though the dust-proof cover on the housing toward a screen disposed outside the housing; and an anti-reflection film formed a light incident surface of the dust-proof cover.
 2. The proximity projection-type projector according to claim 1, wherein the anti-reflection film comprises a plurality of areas, each of the plurality of areas corresponding to differing angles of incidence with respect to the light incident surface.
 3. The proximity projection-type projector according to claim 2, wherein the plurality of areas of the anti-reflection film have differing anti-reflection effects on the projection light, such that the anti-reflection effects of the light-incident surfaces of the areas of the cover portion differ depending on the area.
 4. The projector according to claim 3, wherein the cover portion has a substantially rectangular shape in the plan view and the plurality of areas is formed by dividing the light-incident surface into three in the longitudinal direction of the substantially rectangular shape, and the reference area is the central area of the plurality of areas in the longitudinal direction.
 5. The projector according to claim 2, wherein the cover portion has a substantially rectangular shape in the plan view and the plurality of areas is formed by dividing the light-incident surface into two in the short-side direction of the substantially rectangular shape, a process of preventing the reflection of the projection light incident at an angle of incidence within a predetermined range is performed on one of the areas, and a process of preventing the reflection of the projection light incident at an angle of incidence beyond the predetermined range is performed on the other one of the areas.
 6. The projector according to claim 2, wherein the process of preventing the reflection of the projection light is forming an anti-reflection film on the light-incident surface.
 7. The projector according to claim 6, wherein the anti-reflection films overlap with each other at the boundary between adjacent ones of the areas.
 8. The projector according to claim 2, wherein the projection unit includes a wide-angle light forming reflector that converts the projection light into wide-angle light.
 9. The projector according to claim 1, wherein the cover portion has a substantially uniform thickness and the plurality of areas is formed of a central portion and peripheral portions adjacent to the central portion, and the peripheral portions are bent toward the side where the projection light is incident.
 10. The projector according to claim 9, wherein the central portion is formed of a flat surface.
 11. The projector according to claim 10, wherein each of the peripheral portions is formed of a flat surface.
 12. The projector according to claim 11, wherein the central portion has a substantially rectangular shape in the plan view, and the peripheral portions are connected only to a pair of sides of the central portion that face each other.
 13. The projector according to claim 10, wherein the central portion is substantially parallel to a predetermined flat surface of the outer surfaces of the housing.
 14. The projector according to claim 11, wherein each of the peripheral portions is substantially parallel to a predetermined flat surface of the outer surfaces of the housing.
 15. The projector according to claim 9, wherein the projection unit includes a wide-angle light forming reflector that forms wide-angle light.
 16. The projector according to claim 9, wherein the cover portion is inclined in such a way that the surface of the central portion through which the projection light exits faces the illuminated surface.
 17. The projector according to claim 15, wherein the peripheral portions are bent and inclined to the central portion by approximately 90 degrees.
 18. The projector according to claim 16, wherein the peripheral portions are bent and inclined to the central portion by approximately 90 degrees.
 19. The projector according to claim 1, wherein the dust-proof cover is arranged substantially parallel to an installation plane of the projector. 